The invention relates to a process and a device for monitoring and observation of the aging of a catalytic converter in the exhaust gas of internal combustion engines, for example in motor vehicles, and for registration of the times of the largest emission of hazardous materials of the internal combustion engine.
Catalytic converters in the exhaust gas system of internal combustion engines first begin, after reaching a relatively high operating temperature, to convert the hazardous materials in the exhaust gas, i.e., hydrocarbons, carbon monoxide, and nitrogen oxides, largely into non-hazardous materials. In the first time interval after the internal combustion engine is started, the hazardous materials can pass through the catalytic converter in a practically unhindered manner. Therefore, the newer exhaust gas specifications provide for measurement cycles, which especially include cold and warm start-up phases. It is apparent therein that during these measurement cycles the major part of the hydrocarbon emission arises during the cold start phases. In order to reduce the emission of hazardous materials, a low xe2x80x9clight-off temperaturexe2x80x9d of the catalytic converter, and thus after starting, as short as possible a xe2x80x9clight-off timexe2x80x9d without exhaust gas cleaning, must be sought in particular. Many proposals have already been made for reducing the light-off time.
In order to check the operation of the catalytic converter by OBD (on board diagnosis), many tests are made using sensors, especially for hydrocarbons (CHx) and for nitrogen oxides (NOx). Measurements using expensive measurement systems (with flame ionization detectors: FID) show, however, that after commercial, hot, new exhaust gas catalytic converters or ones that have already been used for a longer time, at least the CHx-concentrations are exceptionally small. These concentrations cannot be measured in a fully certain manner, even with the FID, and are much less able to be quantitatively determined using sensors for CHx or NOx thus far known. Therefore, it is also difficult to use these mechanisms to track the aging of the catalytic converter by any gradual increase in the CHx concentration in the exhaust gas after the catalytic converter.
In order to assess the aging of the exhaust gas catalytic converters, a series of processes have been proposed, in which the hazardous materials concentrations in the exhaust gas are not measured directly. Frequently, the necessary oscillation between rich and lean in the fuel supply is not only regulated using a lambda sensor, which is an oxygen sensor, before the catalytic converter, but also, its effect is tracked using a second lambda sensor after the catalytic converter (see German patent publications DE 23 04 622, DE 24 44 334, DE 35 00 594, DE 41 39 560, DE 42 11 116, DE 43 37 793). Therein, certain charging programs on the catalytic converter system and different switching operations of the signals are used in order to be able to assess the functioning ability of the catalytic converter. Furthermore, it has been proposed to monitor the catalytic converter activity with one temperature sensor shortly before the catalytic converter and another one within the catalytic converter (DE 26 43 739). These proposals generally refer to the operating condition of the catalytic converter system and produce no direct statement about the light-off of the catalytic converter.
The aging of the exhaust gas catalytic converter can be noticed, however, especially in the increase of its light-off temperature, and thus also of the light-off time. Therefore, it has already been proposed to determine the light-off temperature of the catalytic converter and to assess the functional ability of the catalytic converter in this way. It is assumed therein that the temperature in the exhaust gas catalytic converter increases more quickly as soon as the conversion begins, so that the light-off temperature as well as the time span until the beginning of the conversion can be read directly from the temperature-time curve and can be compared to predetermined threshold values (DE 42 11 092). It should be advantageous if the temperature is determined particularly in the area of the catalytic converter system, which is decisive for the warm-up emission (DE 43 30 997). However, the light-off temperature is not represented clearly at all in the temperature-time curve; it is possibly blurred by endothermic desorption processes during the light-off. With the gradual aging of the catalytic converter, the light-off temperature is less and less recognizable. Therefore, these processes are evidently not adequate. As a gradual process, the aging cannot be followed, using the processes known thus far, up to the point at which the catalytic converter is declared to be functionally inoperative.
On motor test stands the light-off of the catalytic converter can be clearly observed, using expensive stationary FID-devices, by the drastic drop of the CHx-concentration in the exhaust gas. On board motor vehicles correspondingly repeatedly reliable observations for checking the aging of exhaust gas catalytic converters and the hazardous materials emission have thus far not been possible using simple mechanisms.
It is an object of the invention to eliminate the disadvantages of the prior art, in particular to provide a process with the corresponding device by which the aging of exhaust gas catalytic converters can not only be monitored on occasion, but also over its entire gradual progression, and which at the same time leads to a quantity that is characteristic for individual starting phases or for the total of the hazardous materials emitted in the start phases.
This object is achieved according to the present invention by a process wherein, after the start of the internal combustion engine, the light-off temperature of the catalytic converter is detected, using a temperature measuring sensor in the catalytic converter, as the temperature at which a sensor for oxygen, carbon dioxide, water vapor or combustible materials in the exhaust gas after the catalytic converter indicates the light-off of the catalytic converter by a signal change as a result of a sudden change of the concentration of the material or material mixture for which the sensor is sensitive, and wherein the light-off time is measured from the start-up of the internal combustion engine to the sensor-indicated light-off of the catalytic converter. The light-off temperature is measured at the exact point in time at which the change in the concentration of the material or material mixture in the exhaust gas detected by the sensor goes through an extreme value, where this extreme value can be obtained by calculating the differences of the sensor signals directly measured in equivalently short time intervals, or mathematical expressions calculated therefrom, or concentrations calculated thereby.
The sensor-indicated light-off temperature as well as the light-off time are measured externally in workshops or monitoring stations and/or determined in the motor vehicle and displayed on board. Advantageously, the values determined after every start-up will be continuously saved on board and processed into statements about the aging and hazardous material emission. As a sensor, one is used that requires a shorter time for heating to operating temperature than the exhaust gas catalytic converter and can immediately follow the concentration changes very quickly. If such prerequisites are not provided, the heating up of the sensor to its operating temperature is to be provided before start-up.
It is advantageous if, as the sensor for the determination of the light-off of the catalytic converter, an oxygen sensor is used in which the catalytic activity of the measuring sensor is smaller than the conventional lambda sensors. In particular, it is expedient that the oxygen sensor used be brought to a temperature at which its combustion gas sensitivity is smaller than its oxygen sensitivity.
It is further advantageous if the temperature measuring sensor and/or the sensor is brought only temporarily for individual monitoring measurements in a motor vehicle into positions for determining the light-off temperature and/or the light-off time of the catalytic converter, or that the temperature measuring sensor and/or sensor is installed fixed in the motor vehicle and thereby, after each start-up of the internal combustion engine, the light-off temperature and/or light-off time is determined on board and saved.
Expediently, the increase of the light-off temperature of the catalytic converter above the light-off temperature of the new catalytic converter is used as one value that characterizes the aging of the catalytic converter, or the average of several (for example 5 to 10) light-off temperatures measured one after the other is calculated, and the increase of this average value above the average value at the beginning of the use of the new catalytic converter is used as a value that characterizes the aging of the catalytic converter.
The time from the start of the internal combustion engine up to the light-off of the exhaust gas catalytic converter greatly depends on the temperature of the catalytic converter at the moment of the start-up of the machine. The process according to the invention is, however, to be further advantageously operated in that only the times from the passage of a specified lower temperature of the catalytic converter until reaching the light-off temperature of the catalytic converter in comparison to this time for the new catalytic converter are used as xe2x80x9cbasis-normalized light-off timesxe2x80x9d for characterization of the aging of the catalytic converter, wherein as a lower temperature, a value of 20 to 100 Kelvin above the yearly average of the ambient temperature in the usage region of the motor vehicle, is specified, or that by itself or in addition, the average of several (for example 5 to 10) basis-normalized light-off times of the catalytic converter is calculated, and the increase of the average of the basis-normalized light-off times in comparison to the average value of the basis-normalized light-off times measured at the beginning of the usage of the new catalytic converter, is used as a value characterizing the aging of the catalytic converter.
Expediently, the measurements for performing the process are only triggered if the temperature of the catalytic converter does not exceed a lower temperature that is specified, such that the heat-up time of the sensor used is, in any case, shorter than the light-off time of the catalytic converter.
An additional advantageous embodiment of the process according to the invention consists in that the sum of all measured and saved complete light-off times is calculated and is saved on board as a value characteristic for the major part of the hazardous material emission, and is made readable there and/or in a workshop or monitoring station, and that this sum is divided by the distance travelled by the motor vehicle since the beginning of the measurements, and thus a characteristic value is obtained for the use of the motor vehicle involved.
For the protection of the gas sensor, it is expedient that the heating thereof is switched off or reduced after use in the start phase of the internal combustion engine.
The device according to the invention for performing the process is thus wherein the signal lines of a temperature measuring sensor positioned (at a suitable location) in or on the catalytic converter and a sensor for oxygen, carbon dioxide, water vapor or combustible materials in the exhaust gas arranged after the catalytic converter, as well as a line transmitting the start up of the internal combustion engine, are connected to an evaluation and arithmetic unit that is externally connectable or installed in the motor vehicle and that is equipped to detect the light-off temperature of the catalytic converter and/or the total light-off time and/or the basis-normalized light-off time of the catalytic converter, according to the process to calculate, to save and/or to make externally readable on a monitoring device, arithmetically formed characteristic values for the aging of the catalytic converter and for the major part of the hazardous material emission as well as for an aspect of the usage of the vehicle, and/or to display these values directly on an on-board instrument.
It is expedient that the temperature measuring sensor and/or the sensor and the evaluation and arithmetic unit be constructed as individual parts for use in different motor vehicles, if only occasional checks are planned, or that the temperature measuring sensor and the sensor as well as the evaluation and arithmetic unit be installed fixed in the motor vehicle with registers for determined characteristic data, in particular that the evaluation and arithmetic unit be integrated into a computer located on board the motor vehicle.
Additional details of the process and device for performing the process according to the invention are to be gathered from the dependent claims.
A great advantage of the described process consists in that important data for the aging of the exhaust gas catalytic converter, for hazardous materials emission and for an aspect of the use of the motor vehicle with an internal combustion engine, to which it is applied, are obtained with the use of sensors that are already relatively well known and are obtained by the use of arithmetic techniques known in principle. The process is thus realizable in a relatively easy manner using the given practical experience.
An additional great advantage consists in that the process can be used by workshops and monitoring stations on motor vehicles in which no corresponding measurement system is installed. On the other hand, the process allows, when the device is installed in the motor vehicle, a comfortable constant monitoring of the exhaust gas system by the motor vehicle operator.